Detecting defects on the surface of wafers produced in the semi-conducting industry is a critical part of the whole production process. Efficient detection includes the ability to distinguish between apparent defects, which may include “nuisance” effects or false alarms, and actual defects. Nuisance effects may include conductors having irregular edges and/or cross-sections. Actual defects include shorts between conductors and breaks of a conductor. Detection systems known in the art include “bright field” systems, using specularly reflected radiation from the wafer surface, and “dark field” systems, which use the scattered radiation from the surface. A number of systems known in the art use specific polarizations of the beam irradiating the wafer surface, or polarizing elements in the detection system.
U.S. Pat. No. 5,883,710, to Nikoonahad et al., U.S. Pat. No. 6,081,325, to Leslie et al., and U.S. Pat. No. 6,215,551, to Nikoonahad et al., whose disclosures are incorporated herein by reference, describe surface inspection systems where an incident beam is directed at a low or grazing angle relative to the surface of the wafer. The incident beam may be set to have s, p, left-, or right-handed circular polarization.
U.S. Pat. No. 6,288,780, to Fairley et al., whose disclosure is incorporated herein by reference, describes a wafer inspection system which is able to use either or both a bright field and a dark field image. The bright field is generated by an unpolarized arc lamp. The system includes a dark field illumination module comprising two laser illumination beams, having adjustable grazing angle, light level, and polarizations.
U.S. Patent Application 2003-0184744 to Isozaki et al., whose disclosure is incorporated herein by reference, describes a surface inspection method that illuminates a region with one or two fixed laser beams, so as to illuminate the region at two different angles. A detection system includes a polarizing plate which may be rotated to maximize a signal/noise ratio.